Image lens distortion correcting method

• US 20020057345A1
• Filed: 07/13/2001
• Published: 05/16/2002
• Est. Priority Date: 09/05/2000
• Status: Active Grant

• Current Assignee: Riken
• Original Assignee: Riken
• Inventors: Tamaki, Toru, Yamamura, Tsuyoshi, Ohnishi, Noboru
• Granted Patent: US 6,791,616 B2
• Time in Patent Office: Days
• US Class Current: 348/207.99
• CPC Class Codes: G06T 5/80 Geometric correction
• CPC Class Codes: H04N 23/81 for suppressing or minimising disturbance in the image signal generation

Abstract

There is disclosed an image lens distortion correcting method comprising: an image printing step (A) for printing an arbitrary image I₁ in a computer; an image pickup step (B) for photographing the printed image I₁ with a camera having a lens distortion and obtaining a photographed image I₂ in the computer; a parameter estimating step (C) for obtaining a parameter θ such that the image I₁ is artificially distorted with the parameter θ and an obtained distorted image I₁^ud equals with the photographed image I₂; and an image correcting step (D) for using the obtained parameter θ to correct the image photographed by the camera. Thereby, (1) no correspondence point needs to be given, (2) any special tool or object is not used, and (3) all points on the image are used, so that an internal parameter can automatically be obtained with high precision, and an image lens distortion can be corrected with high precision.

Claims

1. An image lens distortion correcting method comprising:

an image printing step (A) for printing an arbitrary image I₁ in a computer;

an image pickup step (B) for photographing the printed image I₁ with a camera having a lens distortion and obtaining a photographed image I₂ in the computer;

a parameter estimating step (C) for obtaining a parameter θ

such that the image I₁ is artificially distorted with the parameter θ and

an obtained distorted image I₁^ud equals with the photographed image I₂;

and an image correcting step (D) for using the obtained parameter θ

to correct the image photographed by the camera.

2. The image lens distortion correcting method according to claim 1 wherein said parameter θ

comprises a position correction parameter θ

^U for correcting a position, and a distortion correction parameter θ

^d for correcting the distortion.

3. The image lens distortion correcting method according to claim 2 wherein said position correction parameter θ

^u is a parameter for conversion to an image I₁^u with the corrected position from the image I₁, the conversion parameter is obtained in a least-squares method such that a difference r=I₁(p)−

I₁^u(p+u) between a luminance value I₁ (p) of a point p in the image I₁ and a luminance value I₁^u(p+u) of a point p+u in the image I₁^u corresponding to the point p is minimized entirely on the image, and the obtained parameter is used as the position correction parameter θ

^u.

4. The image lens distortion correcting method according to claim 3 wherein said distortion correction parameter θ

^d is a parameter for conversion to the image I₁^u from the distorted image I₁^ud, the conversion parameter is obtained in the least-squares method such that a difference r=I₂(p)−

I₁^u(f(p)) between a luminance value I₂(p) of the point p in the image I₂ and a luminance value I₁^u(f(p)) of a point f(p) in the image I₁^u corresponding to the point p is minimized entirely on the image, and the obtained parameter is used as the distortion correction parameter θ

^d.

5. The image lens distortion correcting method according to claim 4 wherein said parameter estimating step (C) comprises a step of alternately repeatedly using said position correction parameter θ

^u and said distortion correction parameter θ

^d to obtain the parameter θ

.

6. The image lens distortion correcting method according to claim 5 wherein said parameter θ

is a parameter for conversion to the image I₁^ud from the image I₁, the conversion parameter is obtained in a least-squares method such that a difference r=I₁(p)−

I₂(d(p+u(p)) between a luminance value I₁ (p) of a point p in the image I₁ and a luminance value I₂(d(p+u(p)) of a point d(p+u(p)) in the image I₂ corresponding to the point p is minimized entirely on the image, and the obtained parameter is used as the parameter θ

.

7. The image lens distortion correcting method according to claim 4 wherein said image correcting step (D) comprises a step of using the obtained distortion correction parameter θ

^d to correct the image photographed by the camera.